// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "net/spdy/spdy_frame_builder.h"

#include <limits>

#include "base/logging.h"
#include "net/spdy/spdy_bug_tracker.h"
#include "net/spdy/spdy_framer.h"
#include "net/spdy/spdy_protocol.h"

namespace net {

namespace {

    // A special structure for the 8 bit flags and 24 bit length fields.
    union FlagsAndLength {
        uint8_t flags[4]; // 8 bits
        uint32_t length; // 24 bits
    };

    // Creates a FlagsAndLength.
    FlagsAndLength CreateFlagsAndLength(uint8_t flags, size_t length)
    {
        DCHECK_EQ(0u, length & ~static_cast<size_t>(kLengthMask));
        FlagsAndLength flags_length;
        flags_length.length = base::HostToNet32(static_cast<uint32_t>(length));
        DCHECK_EQ(0, flags & ~kControlFlagsMask);
        flags_length.flags[0] = flags;
        return flags_length;
    }

} // namespace

SpdyFrameBuilder::SpdyFrameBuilder(size_t size, SpdyMajorVersion version)
    : buffer_(new char[size])
    , capacity_(size)
    , length_(0)
    , offset_(0)
    , version_(version)
{
}

SpdyFrameBuilder::~SpdyFrameBuilder()
{
}

char* SpdyFrameBuilder::GetWritableBuffer(size_t length)
{
    if (!CanWrite(length)) {
        return NULL;
    }
    return buffer_.get() + offset_ + length_;
}

bool SpdyFrameBuilder::Seek(size_t length)
{
    if (!CanWrite(length)) {
        return false;
    }

    length_ += length;
    return true;
}

bool SpdyFrameBuilder::WriteControlFrameHeader(const SpdyFramer& framer,
    SpdyFrameType type,
    uint8_t flags)
{
    DCHECK_EQ(SPDY3, version_);
    DCHECK(SpdyConstants::IsValidFrameType(
        version_, SpdyConstants::SerializeFrameType(version_, type)));
    bool success = true;
    FlagsAndLength flags_length = CreateFlagsAndLength(
        flags, capacity_ - framer.GetControlFrameHeaderSize());
    success &= WriteUInt16(kControlFlagMask | kSpdy3Version);
    success &= WriteUInt16(
        SpdyConstants::SerializeFrameType(framer.protocol_version(), type));
    success &= WriteBytes(&flags_length, sizeof(flags_length));
    DCHECK_EQ(framer.GetControlFrameHeaderSize(), length());
    return success;
}

bool SpdyFrameBuilder::WriteDataFrameHeader(const SpdyFramer& framer,
    SpdyStreamId stream_id,
    uint8_t flags)
{
    if (version_ == HTTP2) {
        return BeginNewFrame(framer, DATA, flags, stream_id);
    }
    DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
    bool success = true;
    success &= WriteUInt32(stream_id);
    size_t length_field = capacity_ - framer.GetDataFrameMinimumSize();
    DCHECK_EQ(0u, length_field & ~static_cast<size_t>(kLengthMask));
    FlagsAndLength flags_length;
    flags_length.length = base::HostToNet32(static_cast<uint32_t>(length_field));
    DCHECK_EQ(0, flags & ~kDataFlagsMask);
    flags_length.flags[0] = flags;
    success &= WriteBytes(&flags_length, sizeof(flags_length));
    DCHECK_EQ(framer.GetDataFrameMinimumSize(), length());
    return success;
}

bool SpdyFrameBuilder::BeginNewFrame(const SpdyFramer& framer,
    SpdyFrameType type,
    uint8_t flags,
    SpdyStreamId stream_id)
{
    DCHECK(SpdyConstants::IsValidFrameType(
        version_, SpdyConstants::SerializeFrameType(version_, type)));
    DCHECK_EQ(0u, stream_id & ~kStreamIdMask);
    DCHECK_EQ(HTTP2, framer.protocol_version());
    bool success = true;
    if (length_ > 0) {
        // Update length field for previous frame.
        OverwriteLength(framer, length_ - framer.GetPrefixLength(type));
        SPDY_BUG_IF(SpdyConstants::GetFrameMaximumSize(version_) < length_)
            << "Frame length  " << length_
            << " is longer than the maximum allowed length.";
    }

    offset_ += length_;
    length_ = 0;

    // Assume all remaining capacity will be used for this frame. If not,
    // the length will get overwritten when we begin the next frame.
    // Don't check for length limits here because this may be larger than the
    // actual frame length.
    success &= WriteUInt24(capacity_ - offset_ - framer.GetPrefixLength(type));
    success &= WriteUInt8(
        SpdyConstants::SerializeFrameType(version_, type));
    success &= WriteUInt8(flags);
    success &= WriteUInt32(stream_id);
    DCHECK_EQ(framer.GetDataFrameMinimumSize(), length_);
    return success;
}

bool SpdyFrameBuilder::WriteStringPiece16(const base::StringPiece& value)
{
    if (value.size() > 0xffff) {
        DCHECK(false) << "Tried to write string with length > 16bit.";
        return false;
    }

    if (!WriteUInt16(static_cast<uint16_t>(value.size()))) {
        return false;
    }

    return WriteBytes(value.data(), static_cast<uint16_t>(value.size()));
}

bool SpdyFrameBuilder::WriteStringPiece32(const base::StringPiece& value)
{
    if (!WriteUInt32(value.size())) {
        return false;
    }

    return WriteBytes(value.data(), value.size());
}

bool SpdyFrameBuilder::WriteBytes(const void* data, uint32_t data_len)
{
    if (!CanWrite(data_len)) {
        return false;
    }

    char* dest = GetWritableBuffer(data_len);
    memcpy(dest, data, data_len);
    Seek(data_len);
    return true;
}

bool SpdyFrameBuilder::RewriteLength(const SpdyFramer& framer)
{
    return OverwriteLength(framer,
        length_ - framer.GetControlFrameHeaderSize());
}

bool SpdyFrameBuilder::OverwriteLength(const SpdyFramer& framer,
    size_t length)
{
    if (version_ == SPDY3) {
        DCHECK_LE(length,
            SpdyConstants::GetFrameMaximumSize(version_) - framer.GetFrameMinimumSize());
    } else {
        DCHECK_LE(length, SpdyConstants::GetFrameMaximumSize(version_));
    }
    bool success = false;
    const size_t old_length = length_;

    if (version_ == SPDY3) {
        FlagsAndLength flags_length = CreateFlagsAndLength(
            0, // We're not writing over the flags value anyway.
            length);

        // Write into the correct location by temporarily faking the offset.
        length_ = 5; // Offset at which the length field occurs.
        success = WriteBytes(reinterpret_cast<char*>(&flags_length) + 1,
            sizeof(flags_length) - 1);
    } else {
        length_ = 0;
        success = WriteUInt24(length);
    }

    length_ = old_length;
    return success;
}

bool SpdyFrameBuilder::OverwriteFlags(const SpdyFramer& framer, uint8_t flags)
{
    DCHECK_EQ(HTTP2, framer.protocol_version());
    bool success = false;
    const size_t old_length = length_;
    // Flags are the fifth octet in the frame prefix.
    length_ = 4;
    success = WriteUInt8(flags);
    length_ = old_length;
    return success;
}

bool SpdyFrameBuilder::CanWrite(size_t length) const
{
    if (length > kLengthMask) {
        DCHECK(false);
        return false;
    }

    if (offset_ + length_ + length > capacity_) {
        DCHECK(false);
        return false;
    }

    return true;
}

} // namespace net
